You're 28, ten years past being an adult. Kids grow up, and some move away; this is normal. You didn't abandon an invalid.
Your mother, however, may be an emotional invalid. This is harder for outsiders to grasp, and I'm sorry she did that thing with the mirror. That was shaming, and uncalled for. A core emotion of people with BPD (pwBPD) is shame; i.e., I'm a bad person who doesn't deserve to me loved. I think this is a tragic world view. Even more tragic is when is projected upon a child whose mind and persona is still developing. As children, we can often take this with its into adulthood. "You aren't responsible for her feelings." Sounds good, and is true. Easy to process logically, perhaps, but harder to do so emotionally.
Pressure from family can make detaching (owning your own personhood apart from how others may define you) so much harder, and I'm sorry that you're receiving this pressure.
Have you had a chance to look at the lessons and suggested reading at the top of the board?
https://bpdfamily.com/message_board/index.php?topic=108307.0I'd say you're at least at the stage of taking back the power of your own life.
Going NC is certainly an option, but it may be better to withdraw with boundaries. This is one of my favorite discussions on the board, tell us what you think:
BOUNDARIES: Case studies I like how boundaries are tied to our core principles.
Turkish